This invention relates to a method for making improved high impact polymer blends, particularly high impact blends of monovinylidene aromatic polymers with elastomeric polymers.
Heretofore high impact polymer compositions, such as impact polystyrene compositions, have been formed by first making an elastomeric polymer such as polybutadiene or styrene/butadiene copolymer, adding the elastomeric polymer to monovinylidene aromatic monomer such as styrene, and then polymerizing the monovinylidene aromatic monomer to form a graft copolymer comprising a polymer of the monovinylidene aromatic monomer grafted onto the polybutadiene. Also heretofore elastomeric copolymers have been mechanically blended with a monovinylidene aromatic polymer to improve impact resistance of the latter.
In the latter instance involving mechanical blending of the polymers, experience has shown that one or more properties of the polystyrene such as impact strength cannot be improved without substantial sacrifice of one or more other, often equally important, properties such as tensile strength and flexural modulus. In order to achieve improvement in impact strength while eliminating or at least minimizing the loss of other physical properties, low amounts of high performance rubbers such as the block copolymers of styrene and butadiene have been blended with the polystyrene.
However, even in view of such improved blends, it remains highly desirable to provide blends having further improved impact strength while retaining tensile strength and modulus comparable to polystyrene.